U.S. patent number 8,452,212 [Application Number 13/015,886] was granted by the patent office on 2013-05-28 for charging member, process unit cartridge, and image forming apparatus.
This patent grant is currently assigned to Fuji Xerox Co., Ltd.. The grantee listed for this patent is Minoru Rokutan, Shogo Tomari. Invention is credited to Minoru Rokutan, Shogo Tomari.
United States Patent |
8,452,212 |
Rokutan , et al. |
May 28, 2013 |
Charging member, process unit cartridge, and image forming
apparatus
Abstract
A charging member includes a conductive metal shaft and a
conductive elastic layer. The conductive elastic layer comprises a
rubber material containing 50% to 100% by weight of epichlorohydrin
rubber containing 56 mol % or more of an ethylene oxide and a
calcium oxide having an average particle size D50 of 18 .mu.m or
smaller.
Inventors: |
Rokutan; Minoru (Kanagawa,
JP), Tomari; Shogo (Kanagawa, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Rokutan; Minoru
Tomari; Shogo |
Kanagawa
Kanagawa |
N/A
N/A |
JP
JP |
|
|
Assignee: |
Fuji Xerox Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
45817876 |
Appl.
No.: |
13/015,886 |
Filed: |
January 28, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120070193 A1 |
Mar 22, 2012 |
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Foreign Application Priority Data
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Sep 21, 2010 [JP] |
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2010-210869 |
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Current U.S.
Class: |
399/176 |
Current CPC
Class: |
G03G
15/0233 (20130101); G03G 2215/0132 (20130101) |
Current International
Class: |
G03G
15/02 (20060101) |
Field of
Search: |
;399/174,176
;492/18,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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A-9-297454 |
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Nov 1997 |
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JP |
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A-2006-117870 |
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May 2006 |
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JP |
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Primary Examiner: Royer; William J
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. A charging member comprising: a conductive metal shaft; and a
conductive elastic layer on the shaft, wherein the conductive
elastic layer comprises: a rubber material; and a calcium oxide
having an average particle size D50 of 18 .mu.m or smaller, and
wherein the rubber material contains 50% to 100% by weight of
epichlorohydrin rubber containing 56 mol % or more of an ethylene
oxide.
2. The charging member according to claim 1, wherein the rubber
material contains 50% to 100% by weight of epichlorohydrin rubber
containing 60 mol % or more of an ethylene oxide.
3. The charging member according to claim 1, wherein the rubber
material contains 50% to 100% by weight of epichlorohydrin rubber
containing 70 mol % or more of an ethylene oxide.
4. The charging member according to claim 1, wherein the calcium
oxide is present in an amount of 1 to 15 parts by weight based on
100 parts by weight of the rubber material.
5. The charging member according to claim 1, wherein the calcium
oxide is present in an amount of 3 to 10 parts by weight based on
100 parts by weight of the rubber material.
6. The charging member according to claim 1, wherein the calcium
oxide having an average particle size D50 of 14 .mu.m or
smaller.
7. The charging member according to claim 1, wherein the calcium
oxide having an average particle size D50 of 6 .mu.m or
smaller.
8. A removable process unit cartridge comprising: an image carrier;
and a charging unit being in contact with the image carrier and
adapted to charge the surface of the image carrier, wherein the
charging unit comprises the charging member according to claim
1.
9. An image fowling apparatus comprising: an image carrier; and a
charging unit being in contact with the image carrier and adapted
to charge the surface of the image carrier, wherein the charging
unit comprises the charging member according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
The present application claims priority from Japanese Patent
Application No. 2010-210869 filed on Sep. 21, 2010, the entire
content of which is incorporated herein by reference.
BACKGROUND
1. Field
The present invention relates to a charging member, a process unit
cartridge, and an image forming apparatus.
2. Description of the Related Art
Conventional electrophotographic image forming apparatus, such as
copiers and printers, have mostly used a charger utilizing a corona
discharge phenomenon, such as a scorotron. However, such chargers
generate ozone and nitrogen oxides. Therefore, as a charger used
for electrophotographic image forming apparatus, contact type
chargers that an image carrier is charged by having a conductive
charging member in direct contact with the image carrier have
recently prevailed.
There is an increasing demand for a less resistant charging member
for use in contact type chargers from the viewpoint of higher
speed, higher image quality, and longer life. A charging member has
been produced by a method in which a rubber material is shaped by
pressing or injection molding, and is vulcanized, and then shaped
molding is ground so as to obtain a desired shape and surface
roughness. In recent years, the users' demand for cost reduction
has boosted the use of lower cost processing techniques, including
extrusion molding that achieves good productivity, omission of the
grinding to reduce the number of the manufacturing steps, and
vulcanization at atmospheric pressure that can be carried out with
inexpensive equipment.
Methods for making a charging member include a molding method using
a mold such as injection molding, a method in which an unvulcanized
rubber is extruded into a tube, vulcanizing the extruded tube, and
inserting a cylindrical metal shaft into the tube, and a method in
which an extruder is equipped with a crosshead die, and an
unvulcanized rubber covers a metal shaft, and then vulcanized. The
latter two of the methods are becoming predominant, in which a
rubber cylinder is obtained using an extruder that favors the
reduction of processing cost.
SUMMARY
<1> A charging member having: a conductive metal shaft; and a
conductive elastic layer on the shaft, wherein the conductive
elastic layer has: a rubber material; and a calcium oxide having an
average particle size D50 of 18 .mu.m or smaller, wherein the
rubber material contains 50% to 100% by weight of epichlorohydrin
rubber containing 56 mol % or more of an ethylene oxide.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 schematically illustrates the configuration of an image
forming apparatus according to the invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following describes exemplary embodiments of the charging
member, the process unit cartridge, and the image forming apparatus
according to the invention.
[Charging Member]
The charging member according to the invention includes a
conductive metal shaft and a conductive elastic layer. The
conductive elastic layer has a rubber material containing 50% to
100% by weight of an epichlorohydrin rubber containing at least 56
mol % of ethylene oxide and a calcium oxide having an average
particle size D50 of 18 .mu.m or smaller.
When an epichlorohydrin rubber having an ethylene oxide unit is
used as the conductive elastic layer provided in the charging
member, the conductive elastic layer having lower resistance and
reduced variation in resistance than other rubbers. An increase in
ethylene oxide content will result in further reduction in
resistance of the charging member. However, because ethylene oxide
is hydrophilic, too high an ethylene oxide content in the
epichlorohydrin rubber can cause vaporization of more water content
than necessary during extrusion, resulting in excessive foaming. It
is likely to follow that the extruded layer has larger surface
roughness than intended. Then, in the present invention, an
epichlorohydrin rubber contains at least a specific amount of
ethylene oxide is used to make a charging member having
predetermined low resistance, and a calcium oxide having an average
particle size D50 of 18 .mu.m or smaller and having predetermined
specific surface area, which absorbs excess of the water content in
the rubber material.
The epichlorohydrin rubber that can be used in the invention
contains at least 56 mol %, preferably 60 mol % or more, more
preferably 70 mol % or more, of ethylene oxide. By conducting
vulcanization of the rubber material containing epichlorohydrin
rubber used in the invention, the unvulcanized rubber material
containing the ethylene oxide-containing epichlorohydrin rubber
provides a charging member having high-speed operability, an
extended life, and reduced resistance variation. If the ethylene
oxide content in the epichlorohydrin rubber is less than 56 mol %,
a predetermined resistance cannot be obtained. Also, the rubber
material can contain well-known rubber materials other than the
epichlorohydrin rubber containing ethylene oxide in amount of 56
mol % or more. For example, liquid acrylonitrile butadiene
copolymer rubber or epichlorohydrin rubber containing ethylene
oxide in amount of less than 56 mol % can be preferably used.
Calcium oxide used in the conductive elastic member of the charging
member has an average particle size D50 of 18 .mu.m or smaller,
preferably 14 or smaller, more preferably 6 .mu.m or smaller. The
calcium oxide is preferably present in an amount of 1 to 15 parts,
more preferably 3 to 10 parts, by weight based on 100 parts by
weight of the rubber material. With the calcium oxide content
falling within the ranges, excessive foaming during vulcanization
is prevented, and the vulcanized and molded rubber material
exhibits satisfactory surface properties without needs of
grinding.
The particle size of the calcium oxide to be added is determined
with a particle size analyzer, for example, a laser diffraction
particle size analyzer SALD-2000 available from Shimadzu Corp. The
particle size of the calcium oxide present in the conductive
elastic layer is determined by observing a cross-section of the
conductive elastic member using, for example, a scanning electron
microscope or a transmissive electron microscope.
The charging member of the invention preferably has a ten point
average surface roughness Rz of 15 .mu.m or less, more preferably
10 .mu.m or less, even more preferably 8 .mu.m or less, to control
the variations in resistance and charge of the charging member.
The ten point average surface roughness Rz was measured with a
surface profilometer SURFCOM 1500DX-12 from Tokyo Seimitsu Co.,
Ltd. in accordance with JIS B0601-1994.
While the charging member of the invention may be produced by any
method, for example, if not metal molding method but extrusion
molding method is used, the rubber material containing the
epichlorohydrin rubber may be vulcanized at atmospheric pressure,
and the step of grinding may be omitted. As compared with shaping
in a metal molding, extrusion molding is highly productive and
requires less capital investment and less operational cost for the
production of the charging member.
If desired, the conductive elastic layer may have a stain proof or
bleed proof surface layer. Such a surface layer may suitably be
provided by any general coating technique, such as dip coating,
spraying, roller coating, or flow coating, or by putting a tube
over the elastic layer.
The metal shaft of the charging member is usually made of iron,
copper, brass, stainless steel, aluminum, nickel, or the like. A
free cutting steel shaft as shown in JIS G4804 plated with
chromium, nickel, or the like may also be used. The conductive
metal shaft may be either roll or hollow in shape.
Examples of the vulcanizing agent used to vulcanize the rubber
material include sulfur and compounds that withdraw a halogen group
to achieve crosslinking, such as 2,4,6-trimercapto-s-triazine and
6-methylquinoquixaline-2,3-dithiocarbamate. Examples of useful
vulcanization accelerators include thiazoles series, sulfonamides
series, thiurams series, dicarbamic acid salts series, and
xanthogenic acid salts series. Both the vulcanizing agents and the
vulcanization accelerators may be used individually or as a
combination of two or more thereof. The rubber material may further
be combined with known rubber compounding materials, such as zinc
oxide and stearic acid.
The conductive elastic layer may further contain an organic ion
conductive substance. Examples of the organic ion conductive
substance include quaternary ammonium salts, such as a perchlorate,
a chlorate, a tetrafluoroborate, a sulfate, an ethosulfate, and a
halogenated benzyl salts (e.g., benzyl bromide and benzyl chloride)
of lauryltrimethylammonium, stearyltrimethylammonium,
octadodecyltrimethylammonium, dodecyltrimethylammonium,
hexadecyltrimethylammonium, benzyltrimethylammonium,
benzyltriethylammonium, benzyltributylammonium,
benzyltrioctylammonium, or modified fatty
acid-dimethylethylammonium; aliphatic sulfonic acid salts, higher
alcohol sulfuric ester salts, higher alcohol ethylene oxide adduct
sulfuric ester salts, higher alcohol phosphoric ester salts, higher
alcohol ethylene oxide adduct phosphoric ester salts; various
betaines; higher alcohol ethylene oxide adducts, polyethylene
glycol fatty acid esters, and polyhydric alcohol fatty acid
esters.
Further included in the organic ion conductive substance are
complexes of polyhydric alcohols (e.g., 1,4-butanediol, ethylene
glycol, polyethylene glycol, and propylene glycol) or their
derivatives and metal salts, and complexes of monools (e.g.,
ethylene glycol monomethyl ether and ethylene glycol monoethyl
ether) and metal salts. Examples of the metal salts include salts
of Group 1 of the Periodic Table, such as LiClO.sub.4,
LiCF.sub.3SO.sub.3, LiAsF.sub.6, LiBF.sub.4, NaClO.sub.4, NaSCN,
KSCN, and NaCl; electrolyte, such as NH.sup.4+ salts; salts of
Group 2 of the Periodic Table, such as Ca(ClO.sub.4).sub.2 and
Ba(ClO.sub.4).sub.2; and derivatives of these metal salts having at
least one active hydrogen-containing group reactive with isocyanate
(such as hydroxyl, carboxyl, or primary or secondary amino). The
complexes described are exemplified by a complex of LiClO.sub.4 and
polyethylene glycol.
The conductive elastic layer preferably has a thickness of about
I/O to 4.5 mm, more preferably 1.5 to 4.0 mm, and a volume
resistivity of 10.sup.3 to 10.sup.14 .OMEGA.cm.
The surface layer is made of a resin containing, according to
necessity, a conducting agent and other additives.
Examples of the resin include acrylic resins, cellulose resins,
polyamide resins, copolymer nylons, methoxymethylated nylon,
ethoxymethylated nylon, polyurethane resins, polycarbonate resins,
polyester resins, polyethylene resins, polyvinyl resins,
polyallylate resins, styrene butadiene resins, melamine resins,
epoxy resins, urethane resins, silicone resins, fluororesins (e.g.,
tetrafluoroethylene perfluoroalkyl vinyl ether copolymers,
tetrafluoroethylene hexafluoropropylene copolymers, and
polyvinylidene fluoride), and urea resins. The term "copolymer
nylon" denotes a copolymer composed of at least one polymer unit
selected from nylon 610, nylon 11, and nylon 12. The copolymer
nylon may contain other polymer units, such as nylon 6 and nylon
66. The resin for the surface layer may be the same rubber material
as used to form the conductive elastic layer.
Examples of the additives include those commonly used in a surface
layer, such as softeners, plasticizers, curing agents, vulcanizing
agents, vulcanization accelerators, antioxidants, surfactants, and
coupling agents.
The surface layer preferably has a thickness of 3 to 25 .mu.m and a
volume resistivity of 10.sup.3 to 10.sup.14 .OMEGA.cm.
The surface layer is provided on the conductive elastic layer by,
for example, blade coating, Meyer bar coating, spraying, dip
coating, bead coating, air knife coating, or curtain coating.
The image forming apparatus according to the invention will be
described with reference its exemplary embodiment illustrated in
FIG. 1.
In the image forming apparatus 200 of FIG. 1, four
electrophotographic photoreceptors 401a, 401b, 401c, and 401d are
arranged in series along the moving direction of an intermediate
transfer belt 409 in a housing 400. The photoreceptors 401a, 401b,
401c, and 401d are adapted to form, for example, a yellow, a
magenta, a cyan, and a black color image, respectively.
Each of the photoreceptors 401a to 401d is rotatably driven in
predetermined direction (anticlockwise direction in FIG. 1), and
along with the direction of rotation thereof, a charging roller
402a, 402b, 402c, or 402d, a developing unit 404a, 404b, 404c, or
404d, a first transfer roller 410a, 410b, 410c, or 410d, and a
cleaning blade 415a, 415b, 415c, or 415d are arranged. Toners of
four colors, e.g., yellow, magenta, cyan, and black, are supplied
from the respective toner cartridges 405a, 405b, 405c, and 405d to
the respective developing units 404a to 404d. The first transfer
rollers 410a to 410d are in contact with the respective
photoreceptors 401a to 401d via the intermediate transfer belt
409.
At a prescribed position in the housing 400 is placed an exposure
unit 403 that applies a light beam to the surface of the charged
photoreceptors 401a to 401d. By this configuration, charging,
exposure, development, first transfer, and cleaning are performed
on each rotating photoreceptor 401a to 401d, and the toner images
of four different colors on the photoreceptors 401a to 401d are
sequentially deposited in superimposed registration on the
intermediate transfer belt 409.
The charging rollers 402a to 402d are in contact with the
peripheral surface of the respective photoreceptors 401a to 401d
and uniformly apply a voltage to the respective 401a to 401d to
charge the surface of the 401a to 401d to a predetermined potential
(charging step).
The exposure unit 403 may be an optical device capable of imagewise
exposure by applying light beam from a light source, such as a
semiconductor laser, a light emitting diode, or a liquid crystal
shutter, to the surface of the photoreceptors 401a to 401d. In
particular, an exposure unit that emits incoherent light is
preferred to prevent an interference fringe from occurring between
the conductive substrate and the photosensitive layer of the
photoreceptors 401a to 401d.
The developing units 404a to 404d may be of any type in which a
two-component developer for developing an electrostatic latent
image is used in a contact or non-contact manner to visualize the
latent image with a toner (development step). Also, developer in
the invention may be not limited to a two-component developer. The
developing units 404a to 404d may be chosen from known developing
devices using the two-component developer depending on any purpose.
In the first transfer step, a first transfer bias of opposite
polarity to the toner adhering to the photoreceptors 401a to 401d
is applied to the first transfer rollers 410a to 410d, whereby the
toner images of different colors are sequentially transferred from
the 401a to 401d to the intermediate transfer belt 409.
The cleaning blades 415a to 415d remove residual toners adhering to
the surface of the respective 401a to 401d after the first transfer
so that the 401a to 401d may be subjected to the next cycle of
image formation as described above. The cleaning blades 415a to
415d may be made of urethane rubber, neoprene rubber, silicone
rubber, or the like material.
The intermediate transfer belt 409 is supported by a driving roller
406, a tension roller 407, and a backup roller 408 with
predetermined tension, and thereby the intermediate transfer belt
409 can rotate without sagging by rotating of these roller these
rollers. A second transfer roller 413 is disposed in contact with
the backup roller 408 via the intermediate transfer belt 409.
A second transfer bias of polarity opposite to the toner on the
intermediate transfer belt 409 is applied to the second transfer
roller 413, whereby the second transfer roller 413 transfers the
multi-colored toner image on the intermediate transfer belt 409
onto a recording medium 500 such as paper. The intermediate
transfer belt 409 having passed between the backup roller 408 and
the second transfer roller 413 is cleaned by, for example, a
cleaning blade 416 placed close to the driving roller 406 or an
unshown discharger to be ready for the next cycle of image
formation process. Disposed at a prescribed position in the housing
400 is a transfer receiving medium container 411 (e.g., a paper
feed tray) for feeding a transfer receiving medium 500 (e.g., a
sheet of paper). A transfer receiving medium 500 from the container
411 is transported by transport rollers 412 between the
intermediate transfer belt 409 and the second transfer roller 413
and then between a pair of fixing rollers 414 in contact with each
other and supplied out of the housing 400.
The process cartridge according to the invention includes the
charging member of the invention as a charging roller as shown in
the embodiment illustrated in FIG. 1. For example, a process
cartridge for yellow image formation includes the charging roller
402a, the photoreceptor 401a, the cleaning blade 415a, and the
developing unit 404a; a process cartridge for magenta image
formation includes the charging roller 402b, the photoreceptor
401b, the cleaning blade 415b, and the developing unit 404b; a
process cartridge for cyan image formation includes the charging
roller 402c, the photoreceptor 401c, the cleaning blade 415c, and
the developing unit 404c; and a process cartridge for black image
formation includes the charging roller 402d, the photoreceptor
401d, the cleaning blade 415d, and the developing unit 404d.
EXAMPLE
The invention will be illustrated in more detail with reference to
Examples in which the charging member is a charging roller, but it
should be understood that the invention is not limited thereto.
Unless otherwise noted, all the parts are given by weight.
Evaluations in the following examples and comparative examples are
performed by the following methods. Also, it will be explained to
hold a charging roller as an example of a charging member.
Examples 1 to 11 and Comparative Examples 1 to 3
1. Making Charging Roller
1-1. Making Metal Shaft
A drawn metal tube having an outer diameter of 8 mm is cut to a
length of 330 mm and electroless plated with nickel to make a metal
shaft.
1-2. Formation of Conductive Elastic Layer
The components shown in Tables 1 and 2 below (given in the weight
ratio shown) are kneaded in a tangential type pressure kneader
having a net chamber volume of 75 liters (from Moriyama Co., Ltd.),
and then in a 22-inch open roll mill to obtain an unvulcanized
rubber sheet. The unvulcanized rubber sheet is extruded from a
single screw rubber extruder (cylinder inner diameter: 60 mm; L/D:
20) having a crosshead die (inner diameter: 12 mm; nipple diameter:
8 mm), through which the metal shaft passed continuously, and is
thereby coated with the extruded unvulcanized rubber. The
rotational speed of the screw is 15 rpm, and the extruder
temperatures at the cylinder, screw, head, and die are all set at
80.degree. C. The extruded unvulcanized rubber is vulcanized in an
oven at 180.degree. C. for 30 minutes at atmospheric pressure to
form a conductive elastic layer.
TABLE-US-00001 TABLE 1 Example No. Trade Name Manufacturer 1 2 3 4
5 6 7 8 9 10 11 Epichlorohydrin Epion 301 DAISO CO., 90 90 90 90 90
90 90 90 90 -- -- Rubber LTD. Epichlomer DAISO CO., -- -- -- -- --
-- -- -- -- 90 -- DG LTD. Epichlomer DAISO CO., -- -- -- -- -- --
-- -- -- -- 90 CG102 LTD. Ethylene oxide content 73 73 73 73 73 73
73 73 73 60 56 (mol %) Liquid N280 JSR 10 10 10 10 10 10 10 10 10
10 10 Acrylonitrile Corporation Butadiene Copolymer Rubber Calcium
Oxide Calfine CO., Flime -- Flime Flime Flime Flime Flime Flime
Flime Flime Flime LTD. 400 900 1300 2000 2000 2000 2000 2000 2000
2000 -- Ohmi Chemical -- CML- -- -- -- -- -- -- -- -- -- Industry
Co., 31 Ltd. D50 (.mu.m) 18 14 6 4 1.7 1.7 1.7 1.7 1.7 1.7 1.7
Amount 5 5 5 5 5 1 3 10 15 5 5 Zinc Oxide Zinc Oxide 2 Seido Kagaku
5 5 5 5 5 5 5 5 5 5 5 Industry Co., Ltd. Stearic Acid Stearic Kao 1
1 1 1 1 1 1 1 1 1 1 Acid S Corporation Carbon 3030B Mitsubishi 15
15 5 15 15 15 15 15 15 15 15 Chemical Corporation Quaternary KS-555
Kao 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Ammonium Salt
Corporation Calcium Hakuenka Shiraishi 30 30 30 30 30 30 30 30 30
30 30 Carbonate CC Kogyo Kaisha, Ltd. Vulcanizing Sulfax200 Tsurumi
1 1 1 1 1 1 1 1 1 1 1 Agent Chemical Industry Co., Ltd.
Vulcanization Nocceler Ouchi Shinko 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5
1.5 1.5 1.5 Accelerator A DM-P Chemical Industrial Co., Ltd.
Vulcanization Nocceler Ouchi Shinko 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.5 0.5 0.5 Accelerator B TET Chemical Industrial Co., Ltd.
TABLE-US-00002 TABLE 2 Comparative Example Trade Name Manufacturer
1 2 3 Epichlorohydrin Epion 301 DAISO CO., LTD. -- 90 -- Rubber
Epichlomer DAISO CO., LTD. 90 -- 90 CG105 Ethylene oxide content
(mol %) 48 73 48 Liquid N280 JSR Corporation 10 10 10 Acrylonitrile
Butadiene Copolymer Rubber Calcium Oxide Calfine CO., LTD. Flime
Flime Flime 100 100 400 D50 (.mu.m) 28 28 18 Amount 5 5 5 Zinc
Oxide Zinc oxide class 2 Seido Kagaku Industry 5 5 5 Co., Ltd.
Stearic Acid Steraric Acid S Kao Corporation 1 1 1 Carbon 3030B
Mitsubishi Chemical 15 15 15 Corporation Quaternary KS-555 Kao
Corporation 1.5 1.5 1.5 Ammonium Salt Calcium Carbonate Hakuenka CC
Shiraishi Kogyo 30 30 30 Kaisha, Ltd. Vulcanizing Agent Sulfax200
Tsurumi Chemical 1 1 1 Industry Co., Ltd. Vulcanization Nocceler
DM-P Ouchi Shinko 1.5 1.5 1.5 Accelerator A Chemical Industrial
Co., Ltd. Vulcanization Nocceler TET Ouchi Shinko 0.5 0.5 0.5
Accelerator B Chemical Industrial Co., Ltd.
1-3. Formation of Surface Layer
The following components are dispersed in a bead mill to prepare a
coating solution. After diluting the solution by adding methanol,
the coating solution is applied to the surface of the conductive
elastic layer (substrate) by dipping the substrate into the coating
solution and thereby coating the substrate with appropriate control
of the initial coating speed and acceleration, followed by drying
by heating at 120.degree. C. for 20 minutes to form a 10 .mu.m
thick surface layer. In this way, the surface layer of the charging
roller is obtained.
Formulation of Surface Layer:
TABLE-US-00003 Copolymer nylon Aramine CM8000 from Toray Co., Ltd.
100 parts Carbon black MONARCH 1000 from Cabot Corp. 14 parts
(conducting agent) Methanol (solvent) 500 parts Butanol (solvent)
240 parts
2. Evaluation of Charging Roller
2-1. Foaming
A cross-section of the conductive elastic layer is observed under a
digital microscope VHX-900 from Keyence Corporation at 25
magnifications to inspect for foaming. The state of foaming is
evaluated as follows.
AA: No foams are observed.
A: One or two foams of 100 .mu.m or smaller in diameter and no foam
greater than 100 .mu.m are observed within a 2 mm.sup.2 area.
B: Three to five foams of 100 .mu.m or smaller in diameter or one
or two foams of 100 to 200 .mu.m in diameter are observed within a
2 mm.sup.2 area.
C: More than six foams of 100 .mu.m or smaller in diameter, or more
than two foams of 100 to 200 .mu.m in diameter, or one or more
foams greater than 200 .mu.m in diameter are observed within a 2
mm.sup.2 area.
2-2. Surface Roughness (Rz)
The surface roughness in terms of Rz of the charging roller is
determined using a profilometer Surfcom 1500 DX-12 from Tokyo
Seimitsu Co., Ltd. in accordance with JIS B0601-1994 under
conditions of an evaluation length of 4.0 mm, a cut-off value of
0.8 mm, and a scanning speed of 0.30 mm/sec. The measurement is
taken along the axial direction of the roller at three points: 5 mm
from both ends of the roller and the axial center of the roller, to
obtain an average. The surface roughness is evaluated according to
the parameter Rz as follows.
AA: Rz of 8 .mu.M or less.
A: Rz of more than 8 .mu.m and not more than 10 tam.
B: Rz of more than 10 .mu.m and not more than 15 .mu.m.
C: Rz of more than 15 .mu.m.
2-3. Volume Resistance
The unvulcanized rubber sheet obtained in aforementioned 1-2 is
shaped in a press at 180.degree. C. for 30 minutes into a 150 mm by
150 mm by 2 mm thick sheet, After seasoning the sheet at 22.degree.
C. and 55% RH for at least 24 hours, the volume resistance of the
sheet is measured using a digital ultra-high resistance/micro
current meter (Model R8340A, from ADC Corp.), a UR probe
(MCP-HTP12, from Dia Instruments) having a double ring-electrode
structure the connector of which is modified in conformity to
R8340A, and a Resitable UFL MCP-ST03 (from Mitsubishi Chemical
Analytech Co., Ltd.) in accordance with JIS K6911 under conditions
of a charge time of 30 seconds, a discharge time of 1 second, and
an applied voltage of 100 V. The measured volume resistance is
evaluated as follows.
AA: A common logarithm of the resistance (log .OMEGA.cm) is less
than 6.5.
A: A common logarithm of the resistance (log .OMEGA.cm) is 6.5 or
more and less than 7.0.
B: A common logarithm of the resistance (log .OMEGA.cm) is 7.0 or
more and less than 7.5.
C: A common logarithm of the resistance (log .OMEGA.cm) is 7.5 or
more.
2-4. Image Quality
The charging roller is mounted on a copier Apeos Port-IV C5570 from
Fuji Xerox Co., Ltd. A printing test is carried out in a continuous
mode at 28.degree. C. and 85% RH to obtain 25,000 sheets of A4 size
prints and subsequently at 10.degree. C. and 15% RH to obtain
25,000 sheets of A4 size prints. When any serious trouble occurred
before accomplishing a total of 50,000 prints, the test is stopped
at that time. The initial print and the print after the 50,000
prints are visually inspected for density unevenness in the
halftone image area to evaluate the image quality according to the
following rating system.
AA: No image defects such as density unevenness.
A: Very slight density unevenness.
B: Slight density unevenness.
C: Practically unacceptable density unevenness.
The results of evaluations are shown in Tables 3 and 4.
TABLE-US-00004 TABLE 3 Example 1 2 3 4 5 6 7 8 9 10 11 Ethylene
Oxide Content 73 73 73 73 73 73 73 73 73 60 56 (mol %) Particle
Size D50 of 18 14 6 4 1.7 1.7 1.7 1.7 1.7 1.7 1.7 Calcium Oxide
(.mu.m) Calcium Oxide Content 5 5 5 5 5 1 3 10 15 5 5 (part)
Foaming B A AA AA AA B AA AA AA AA AA Rz A A AA AA AA AA AA AA B AA
AA Volume Resistance AA AA AA AA AA AA AA AA AA A B Density
Unevenness A A AA AA AA AA AA AA B A B
TABLE-US-00005 TABLE 4 Comparative Example 1 2 3 Ethylene Oxide
Content 48 73 48 (mol %) Particle Size D50 of 28 28 18 Calcium
Oxide (.mu.m) Calcium Oxide Content 3 15 20 (part) Foaming C A AA
Rz B C C Volume Resistance C A C Density Unevenness C C C
INDUSTRIAL APPLICABILITY
The present invention is applicable to electrophotographic image
forming apparatus such as copiers and printers.
While the present invention has been shown and described with
reference to certain exemplary embodiments thereof, it will be
understood by those skilled in the art that various changes
modifications may be made therein without departing from the spirit
and scope of the present invention as defined by the appended
claims.
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